The genetic control, structure and assembly of the membrane-bound nitrate reductase complex is being studied in Escherichia coli. Conditional mutants (temperature sensitive and cold sensitive) are being isolated in an attempt to identify the structural genes of this complex. In addition, the conditional mutants are being utilized to establish the required order of expressions of the seven genes which control the formation of this complex. The final steps in the maturation of the enzyme complex are being studied by investigating the formation of active enzyme and the addition of molybdenum in vivo and in vitro in the absence of protein synthesis. The formation of active forms of the individual components (formate hydrogenase, cytochrome b1 and nitrate reductase) as well as the full chain is being studied in the wild type which has been grown in the presence of tungstate to accumulate inactive forms of the components and in chlD mutants grown in the absence of added molybdate.